Application of luminescence age models to heterogeneously bleached quartz grains from flood deposits in Tamilnadu, southern India: Reconstruction of past flooding

Abstract

High magnitude floods are generally associated with wet periods or shift in climate. Recent events of increased flooding in southern India raises the question of these to be either associated with human impact or a general climate shift. Due to lack of instrumental/historical records beyond a certain period, one need to look for fluvial records e.g. slack water deposit, levees deposit and signature of high discharge events. Luminescence dating dates the last daylight exposure of sediments. Therefore, dating of young extreme fluvial events may be challenging due to presence of significant remnant geological luminescence resulting in overestimation of ages. The present work examines this in a variety of fluvial deposits e.g. channel sediment, overbank deposit and flood plain deposits of ephemeral system of rivers in southern India to reconstruct past flooding events. The study demonstrated successful application of various age models often used in optical dating i.e. Common Age model (CAM), Minimum Age Model (MAM) and least 5% on the calculated equivalent doses obtained in heterogeneously bleached sediment and suggests that optical dating of fluvial sediments with heterogeneous bleaching can give dependable outcomes when proper age models are utilized. Results suggests duration of the extreme floods occurred during 50–60, 100–120, 180–200, 280–300 and 750–800 years ago. The gap indicates effect of Little Ice Ages (LIA) and several flooding events at 750–800 years ago indicate the end of Medieval Warm Period (MWP). The results indicate that the flooding events increase at the boundary of major climatic changes probably because these changes are associated with an increase in the depressions and cyclonic activity. The recent increase in flooding events which are associated with depressions and cyclonic activity could be an early warning of either a major climate shift or human impact.